It is well-known in the art that electromagnetic waves in the radio frequency spectrum may be linearly, elliptically or circularly polarized. Linearly polarized electromagnetic waves are confined to a single plane extending in the direction of wave propagation and may be oriented at any angle. Electromagnetic waves that are either circularly or elliptically polarized comprise a linear wave rotated about the axis of wave propagation in either a clockwise or counter-clockwise manner. The major axis of an elliptically polarized wave may be orientated at any angle in a manner similar to a linearly polarized wave.
In military applications, it is important that information on the incident electromagnetic wave type, that is, orientation and rotation, be determined as quickly as possible. This information provides an important parameter identifying the signature, or fingerprint, of the electromagnetic wave emitter. Once the wave information has been identified, the emitter that generated the incident electromagnetic wave can be recognized from its signature for purposes of intelligence gathering, homing, emitter sorting, interference reduction, or configuration of an active electromagnetic wave jammer.
Historically, polarimeters have been constructed of a dual channel receiver coupled to a dual orthogonally polarized antenna to measure the power of the polarization components of the incident electromagnetic wave. The measured power of these components identifies the polarization characteristics of the electromagnetic waves. A conventional polarimeter comprises an orthogonally polarized antenna coupled to a pair of phase and gain matched receivers. Identification of the type, orientation and rotation of the incident wave is accomplished by comparing the relative amplitude and phase of the output signals from the dual receivers.
In addition to identifying the type, orientation, and rotation of the incident electromagnetic wave, a polarimeter system must be capable of sensing the total energy in the incident polarized electromagnetic wave with as little energy loss as possible. In conventional dual channel receivers, a dual orthogonally polarized antenna receives from zero to one hundred percent of the energy in an incident polarized electromagnetic wave depending on the antenna's coupling coefficient to the electromagnetic wave's polarization. The pair of phase and gain matched receivers of the conventional dual channel receiver individually output two separate signals representing the energy in each of the two orthogonally polarized wave components. These two orthogonally polarized wave components always sum to one hundred percent of the incident polarized electromagnetic wave's energy if there is no energy loss in the system. The lower the energy loss in the system during the recovery of the energy of the incident polarized electromagnetic wave the greater will be the signal to noise ratio.
This conventional approach to polarimeter construction has proven to be unsatisfactory as it requires interconnecting two complex and costly phase and gain matched receivers. A further drawback of dual channel matched receiver polarimeters is that the second receiver adds weight to the apparatus and requires additional mounting space. In weight and space sensitive applications, for example, in military aircraft, the weight and space necessary to provide a second receiver for the polarimeter may not be available or, if available, is provided at the expense of other important system components.
Accordingly, there is a need for a signal processing technique for polarization detection that eliminates the need for complex and costly dual channel receivers. There is also a need for a signal processing technique for a polarization detection system that senses the total energy in the incident polarized electromagnetic wave without the need for complex and costly dual channel receivers.